The present invention relates to an apparatus for winding wire into a coil in an annular groove formed in the internal surface of a cylindrical body such as a rotor of a rotary transformer.
In a conventional method for forming a coil in an annular groove defined in the internal surface of a cylindrical body, wire is preliminarily wound outside of the cylindrical body into a series of annular portions, the annular portions of the wound wire are fixed together by a self-melt bonding technique and are formed into a coil, and thereafter the coil is inserted into the cylindrical body while being deformed until the coil is received in the annular groove of the body- This method has drawbacks in that it is inefficient because of the many processing steps required and in that the quality of the final products is not uniform.
To overcome these drawbacks, Japanese Laid-open Patent Publication No. 61-100911 proposes a method in which wire having a bonding agent preliminarily applied thereto is supplied from a supply nozzle into an annular groove of a cylindrical body, is wound within the groove, and the wire is pressed against the surface of the cylindrical body defining the bottom of the groove by a roller provided behind the supply nozzle in its direction of movement. The wire is thus bonded to the cylindrical body within the annular groove thereof.
However, this method also has drawbacks in that the bonding agent adheres to the roller whereby the coil is thus likely to be wound up on the roller, and in that an end portion of the coil is required to be treated after the bonding agent hardens. Therefore, in another proposed method, the end portion of the coil is lapped (end portion processing) against a connection pin of the cylindrical body and the wire is then wound into a coil in the annular groove of the cylindrical body whereby the bonding agent does not have to be used.
However, since the apparatus for executing the above-described method employs a tension device which imparts a constant tension to the wire as it is being wound into a coil, the winding operation is performed deficiently because the supply nozzle is not able to precisely follow an intricate path during the end portion processing and winding process which are performed in series. Moreover, the wire may become slack resulting in a poorly formed coil.
Meanwhile, it is necessary to position the cylindrical body when conducting the end portion processing. For this purpose, the winding apparatus has been designed to rotate a cylindrical body while pressing the same against a holding base provided with a positioning projection. Rotation of the cylindrical body is stopped when an axial groove defined in internal surface of the cylindrical body receives the positioning projection of the holding base, whereby the cylindrical body is determined to be in a proper relative rotational position. However, there are also drawbacks with this aspect of the prior art in that the cylindrical body may be damaged or chipped and in that the positioning projection is worn so severely that the positioning of the cylindrical body becomes inaccurate.